Host defense against malignant tumors consists of a number of different mechanisms which can be enhanced by both specific and nonspecific immune stimulants. The project is designed to monitor macrophage effector function in tumor-bearing mice and subjected to specific or nonspecific immunological macrophage activation. This will be assessed by measurement of their capacity to mediate cytostasis and cytotoxicity directed against a variety of neoplastic cell lines. Immunologically specific macrophage activation will be measured both by T-cell arming and antibody-dependent, cell-mediated cytotoxicity assays. Immunomodulators such as Levamisole, B.C.G. and C. parvum are potent macrophage "activators"; however, it is apparent that numerous states of macrophage activation exist. It is, therefore, proposed to measure macrophage production of plasminogen activators, prostaglandin, colony stimulating factors and lysozyme as additional parameters of activation and to correlate these with tumoricidal activity. The stimulation of macrophage production may be an important component of the host defense mechanism, and so we propose to monitor macrophage progenitor cells in various hemopoietic tissues of tumor-bearing and immunostimulated mice.